1. Field of the Invention
The present invention relates to the art of opening blast furnace tap holes and to blast furnace tap hole drills, and more particularly to a new and improved blast furnace tap hole drill having a movable support means for supporting the drill rod between the movable percussion drill mechanism and the rod support at the forward end of the feed shell to thereby permit the use of multiple drill rod components.
2. Summary of the Prior Art
It is well known that the hearth of an iron blast furnace is provided with a tap hole, commonly referred to as a "iron notch", through which molten iron, usually referred to as "hot metal", is drawn off at periodic intervals during the blast furnace campaign. During a normal campaign, such tapping must be done on an average of five to twelve times daily as the blast furnace hearth becomes filled with molten iron and slag. After the blast furnace has been tapped; i.e., the molten hot metal and slag drained therefrom, the tap hole or iron notch is plugged with clay or "mud" which will harden and seal the tap hole until the next time the blast furnace is tapped.
In accordance with usual practices, a special drill is utilized to open a tap hole; i.e., drill a passageway through the hardened clay plugging the iron notch for the purposes of tapping the blast furnace. Such blast furnace tap hole drills are normally pneumatically or hydraulically operated rotary percussion drills comparable to the rock drills utilized in the mining industry. Such drills impart both a rotary and an impact force on an elongated drill rod having a rock drill bit at the end towards the iron notch.
The base support for the blast furnace tap hole drill is normally secured to the floor, a structural column, or some solid base structure and is provided with suitable linkage members and remote controls so that the blast furnace tap hole drill can be remotely operated from a safe distance away. Pursuant to such remote operation, the tap hole drill is operated to move the drill into the proper position for drilling the tap hole, then operated to drill the tap hole, and thereafter moved back away from the tap hole and heat of the emerging hot metal, where the drill can be serviced and prepared for the next tap.
To prepare the blast furnace tap hole drill for each succeeding tap, it is always necessary to replace the drill bit, if not the drill rod or a portion thereof. This is because the temperature of the blast furnace hot metal, being about 2700.degree.-2800.degree. F., severely erodes the drill bit after it drills through the clay plug and enters the bath of molten hot metal. In addition, once the tap hole is drilled the ferrostatic head of hot metal within the blast furnace will cause the hot metal to emerge through the tap hole around the drill bit and drill rod before the drill rod and bit can be withdrawn from the tap hole. Often times, the drill bit will not only be severely eroded but the portion remaining will virtually be "welded" to the end of the drill rod to which it had previously been removably attached. In such an event, it will be impossible to remove the drill bit from the drill rod to replace a new drill bit, and accordingly it then becomes necessary to replace the entire drill bit and adjoining drill rod or drill rod component to which it is welded.
To reduce the expense of replacing the entire drill rod and bit assembly, it has become common practice to utilize a drill rod extension, which is merely a removable end portion of the drill rod, typically from 18 to 30 inches in length, fitted between the elongated rearward portion of the drill rod and the drill bit. Therefore, when the drill bit becomes welded to the drill rod extension bar, or the extension bar otherwise damaged, the extension bar can be replaced without the need for replacing the entire drill rod assembly. Since the entire drill rod assembly is normally 11 to 15 feet in length, it is clear that replacement of an 18 to 30 inch extension bar is significantly less costly than replacement of a 11 to 15 foot drill rod. It often happens, however, that even the drill rod is damaged by the heat of the operation and in need of replacement. Since any damage to the drill rod is normally relatively close to the end attached to the extension bar, it is obvious that if the drill rod were to comprise two or more replaceable lengths, in addition to the extension bar, that additional savings could be achieved by merely replacing the forward portion of the drill rod.
Because of the exceptional length of the drill rod assembly, however, it has not been possible to utilize interconnections which are spaced significantly from one or the other of the supported ends. Specifically, if a conventional drill rod were to comprise two rods joined together at or near the mid-length, or even more than say 40 inches from an end support, the rotary and impacting forces acting thereon would tend to cause the rod to buckle at the interconnection and cause the drill bit to advance at an angle deviated from the drill angle intended. Such a deviated drill angle can cause damage to the iron notch as well as other complications in the tapping procedure which can not be tolerated. In fact, it is because of this buckling phenomenon that it is necessary to limit the length of the extension bar to no more than about 30 inches. If longer extension bars are utilized, the tendency for the drill rod assembly to buckle at the coupling interface becomes rather significant.
It has been appreciated that if the drill rod could be supported at or near the mid-length, that the tendency to buckle would be so significantly minimized, that the drill angle would not be adversely affected. However, most tapping procedures require that the percussion drill advance the drill bit by an amount almost equal to the length of the drill rod assembly. Therefore, the percussion drill advances throughout most of the length of the feedshell upon which it is advancing, brings it quite close to the forward rod support, and hence there is no place on the feedshell upon which a mid-length support can be positioned without it restricting the advancing motion of the percussion drill.